• Nuclear Engineering and Technology
• /
• 제52권10호
• /
• pp.2285-2289
• /
• 2020

Protactinium contamination is a mayor issue in the thorium fuel cycle. We investigate, in this work, the consequences of Pa incorporation in vacancy defects and interstitials in Th, ThC and ThN. We calculate charge transfers and lattice distortions due to these incorporations as well as migration paths and energies involved in the diffusion of Pa.

• Journal of Electrochemical Science and Technology
• /
• 제13권1호
• /
• pp.71-77
• /
• 2022

Metal halide perovskites are promising photovoltaic materials, but they still have some issues that need to be solved. Hysteresis is a phenomenon that strongly is correlated with ion migration; thus, a fast, easy, and low-temperature method for measuring ion migration is required. Through selective blocking, ion migration can be measured separately, apart from electron migration. In this study, ion migration in metal halide perovskites was measured using a vertical device. At different temperatures, ionic activation energies were obtained for a range of perovskite compositions such as MAPbI₃, FAPbI₃, CsPbI₃, and MAPbBr₃. By comparing the measured ionic activation energies with the theoretical values, we conclude that among other possibilities, I^- is the migrating ion in MAPbI₃, FAPbI₃, CsPbI₃, and Br- is the migrating in MAPbBr₃.

• 한국세라믹학회지
• /
• 제52권5호
• /
• pp.331-337
• /
• 2015

$LaBO_3$ (B = Cr, Mn, Fe, Co, and Ni) perovskites, the most common perovskite-type mixed ionic-electronic conductors (MIECs), are promising candidates for intermediate-temperature solid oxide fuel cell (IT-SOFC) cathodes. The catalytic activity on MIEC-based cathodes is closely related to the bulk ionic conductivity. Doping B-site cations with other metals may be one way to enhance the ionic conductivity, which would also be sensitively influenced by the chemical composition of the dopants. Here, using density functional theory (DFT) calculations, we quantitatively assess the activation energies of bulk oxide ion diffusion in $LaBO_3$ perovskites with a wide range of combinations of B-site cations by calculating the oxygen vacancy formation and migration energies. Our results show that bulk oxide ion diffusion dominantly depends on oxygen vacancy formation energy rather than on the migration energy. As a result, we suggest that the late transition metal-based perovskites have relatively low oxygen vacancy formation energies, and thereby exhibit low activation energy barriers. Our results will provide useful insight into the design of new cathode materials with better performance.

• 한국전산유체공학회:학술대회논문집
• /
• 한국전산유체공학회 2010년 춘계학술대회논문집
• /
• pp.556-561
• /
• 2010

This paper proposes a three-dimensional haptotaxis model to simulate the migration of the population of cancer cells. The invasion of the cancer cells relates with the hapto- and the effect of the energy between cells and (ECM). The diffuse interface model is employed, which incorporates haptotaxis mechanism and interface energies. The semi-implicit Fourier spectral scheme is adopted for efficient complications. The simulation results reveal rich dynamics of cancer cells migration.

• Bulletin of the Korean Chemical Society
• /
• 제7권4호
• /
• pp.279-282
• /
• 1986

The MNDO calculations were performed in order to investigate the gas-phase reaction mechanism of 2-propene-1-al oxide, as a model compound of dypnone oxide(1,3-diphenyl-2-butene-1-one oxide) with the chloride ion. Optimized geometries and heats of formation for two probable concerted pathways, CHO and H migration, were determined and their activation energies were obtained. MO results show that although the formyl migration is thermodynamically more favorable than the hydride migration, the latter kinetically predominates over the formyl migration, which is contrary to the established migrating preferences. It is concluded that the hydride migratory propensity is catalyzed by the chloride ion by reducing the capability of the carbonyl ${\pi}$ bond to participate in the migration.

• 한국식품영양과학회지
• /
• 제33권6호
• /
• pp.1056-1062
• /
• 2004

발포 폴리스티렌으로부터 증류수로의 잠재적 저분자 물질의 이행을 측정하고 수학적 모델을 이용하여 이행속도를 분석하고 예측하고자 하였다. 총괄 이행의 지표로 사용되는 KMnO$_4$ 소비량, 증발잔류물 등과 특정 이행으로는 styrene monomer를 측정하였다. Fick의 법칙을 사용하여 폴리스티렌으로부터의 이행과 확산에 대한 정량적 모델을 확립하고, 온도 및 용매조건에 따른 확산계수를 구하였다. 이로부터 다양한 사용조건에 대한 이행량을 예측하고, 현실적인 의미를 제시하였다. 발포 폴리스티렌으로부터의 증류수로의 이행물질로서 KMnO$_4$소비량, styrene monomer의 이행은 6$0^{\circ}C$에서 각각 0.030 $\textrm{mm}^2$/h과 6.8${\times}$$10^{-5}$ $\textrm{mm}^2$/h의 값을 보였다. 온도의존성을 나타내는 활성화에너지 값은 KMnO$_4$ 소비량, styrene monomer에 대해 각각 80.5 kJ/㏖ 및 98.6 kJ/㏖로 나타났다. 이행량 측정에서 적절한 이행의 정도를 얻을 수 있는 실험조건을 제시하고, 몇 가지 예상조건에 대해서 styrene monomer의 이행거동을 예측 제시하였다.

• 한국분말재료학회지
• /
• 제25권2호
• /
• pp.109-119
• /
• 2018

The objective of this study is to reveal the sintering mechanism of mixed Ti-6Al-4V powders considering the densification and the homogenization between Ti and Al/V particles. It is found that the addition of master alloy particles into Ti enhances densification by the migration of Al into the Ti matrix prior to the self-diffusion of Ti. However, as Ti particles become coarser, sintering of the powders appears to be retarded due to slower inter-diffusion of the particles due to the reduced surface energies of Ti. Such phenomena are confirmed by a series of dilatometry tests and microstructural analyses in respect to the sintering temperature. Furthermore, the results are also consistent with the predicted activation energies for sintering. The energies are found to have decreased from 299.35 to $135.48kJ{\cdot}mol^{-1}$ by adding the Al/V particles because the activation energy for the diffusion of Al in ${\alpha}-Ti$ ($77kJ{\cdot}mol^{-1}$) is much lower than that of the self-diffusion of ${\alpha}-Ti$. The coarser Ti powders increase the energies from 135.48 to $181.16kJ{\cdot}mol^{-1}$ because the specific surface areas of Ti decrease.

• 한국세라믹학회지
• /
• 제35권4호
• /
• pp.347-354
• /
• 1998

Densification and grain growth behaviors of ITO ceramics were investigated as a function of TiO2 ad-ditions. TiO2 addition led to inhibition of the grain growth and promotion of the densification of ITO ceram-ics. From the microstructure observation it was found that the crack-like voids which were formed in pure ITO specimens decreased with increase of TiO2 additon. The grain growth exponent(n) was measur-ed to be 4 for pure ITO 3 for TiO2-doped ITO specimens respectively. It was supposed that the grain boun-dary migration of pure ITO ceramics was controlled by the pores which were moved by surface diffusion. On the contrary the grain boundary migration of TiO2-doped ITO specimens was depressed by solute drag effect. The activation energies for grain growth were measured to be 1013 kJ/mol for pure ITO ceramics and 460kJ/mol for TiO2-doped ITO specimens respectively.

• Nuclear Engineering and Technology
• /
• 제55권8호
• /
• pp.2879-2888
• /
• 2023

In fusion environments, large scales of helium (He) atoms are produced by a radical transformation along with structural damage in structural materials, resulting in material swelling and degradation of physical properties. To understand its irradiation effects, this paper investigates the stability, electronic structure, energetics, charge density distribution, PDOS and TDOS, and diffusion processes of He impurities in 6HSiC materials. The formation energy indicates that a stable, favorable position for interstitial He is the HR site with the lowest energy of 2.40 eV. In terms of vacancy, the He atom initially prefers to substitute at pre-existing Si vacancy than C vacancy due to lower substitution energy. The minimum energy paths (MEPs) with migration energy barriers are also calculated for He impurity by interstitial and vacancy-mediated diffusion. Based on its calculated energy barriers, the most possible diffusion path includes the exchange of interstitial and vacancy sites with effective migration energies ranging from 0.101 eV to 1.0 eV. Our calculation provides a better understanding of the stabilization and diffusion behaviors of He impurities in 6H-SiC materials.

• 한국세라믹학회지
• /
• 제53권3호
• /
• pp.301-305
• /
• 2016

We investigate proton conduction in a nonstoichiometric ${\Sigma}3$ $BaZrO_3$ (210)[001] tilt grain boundary using density functional theory (DFT). We employ the space charge layer (SCL) and structural disorder (SD) models with the introduction of protons and oxygen vacancies into the system. The segregation energies of proton and oxygen vacancy are determined as -0.70 and -0.54 eV, respectively. Based on this data, we obtain a Schottky barrier height of 0.52 V and defect concentrations at 600K, in agreement with the reported experimental values. We calculate the energy barrier for proton migration across the grain boundary core as 0.61 eV, from which we derive proton mobility. We also obtain the proton conductivity from the knowledge of proton concentration and mobility. We find that the calculated conductivity of the nonstoichiometric grain boundary is similar to those of the stoichiometric ones in the literature.